The present invention relates to catalytic cracking processes for the conversion of a stream of hydrocarbon feed stock under catalytic cracking conditions and more particularly to the testing of catalysts for use in such processes.
In catalytic cracking, a stream of hydrocarbon feed stock is contacted with an active catalyst in a reactor maintained under catalytic cracking conditions with the reaction products being removed from the reactor. The catalyst in the reactor becomes contaminated by the deposition of coke and is removed from the reactor for regeneration. The coke is burned off the spent catalyst in a regenerator by blowing air through the regenerator. The regenerated catalyst is then fed back to the reactor.
The catalytic cracking processes in common use today are described in 1980 REFINING PROCESSES HANDBOOK, reprinted from September, 1980 issue of HYDROCARBON PROCESSING, pp. 145-152. Most of the catalytic cracking processes in use today have an entrained bed reactor wherein feed stock and regenerated catalyst are continuously mixed and flow through the reactor which provides the necessary residence time for cracking. The product is separated from the contaminated catalyst which is then transferred to the regenerator.
Extensive study has been conducted of the properties of catalysts for use in such processes. It is desirable to determine such properties as catalyst aging with time and conversion efficiency under various operating conditions. Small fixed bed reactors are commonly used to screen catalysts. However, fixed bed reactors have certain disadvantages, including the difficulty of regenerating the catalyst in a fixed bed. If the catalyst is quickly burned, local hot spots may be produced which damage the catalysts. If the catalyst is regenerated carefully, it takes a long time to perform the regeneration. Also, fixed bed reactors do not provide the same dynamic operting conditions as entrained bed reactors, and hence do not provide good indications of the performance of the catalyst in an actual entrained bed reaction. In U.S. Pat. No. 4,028,430-Stine, et al, a plurality of fixed bed reactors are connected and operated in a manner which simulates a moving catalyst bed. A suitable programming device charges the points of inlet and outlet into and from the reactor including a reactivation stream of catalysts. This is a relatively large unit which is not suitable for small scale laboratory testing.
The optimum way of testing catalysts would be to provide a scaled-down version of the actual operating reactors and regenerators. However, the actual apparatus is complicated. Pilot plants have been built to simulate the operation of larger catalytic processes. However, it is desirable to provide even smaller apparatus for use in the laboratory to test catalyst properties. One approach to the laboratory screening of catalysts is to provide an entrained bed reactor wherein a charge of feed stock and a charge of catalyst are mixed and fed to a reactor which provides the desired residence time typical of the actual process being simulated. Then the product and contaminated catalyst are fed to a disengagement vessel. Under laboratory conditions, such a run takes a very short time, for example, on the order of ten minutes. Then the catalyst is removed from the disengagement vessel and regenerated. This is time-consuming and does not provide desired information about catalyst performance under extended operating conditions where the catalyst is being continuously supplied to a regenerator and then fed back to the reactor.
Another approach to laboratory testing is the simulation of catalytic cracking processes on general purpose digital computers. U.S. Pat. No. 4,187,548--Gross, et al is an example of digital computer simulation of a catalytic cracking process. While such simulations provide good predictions of the product yield under known operating conditions and with known catalysts, they are not as useful for screening new catalysts under different operating conditions.
It is an object of the present invention to provide apparatus for investigating the performance of catalysts used in entrained bed catalytic cracking process.